# Date Calculator

> Adding days to a date counts forward on the calendar: 90 days after Tuesday, November 10, 2026 is Monday, February 8, 2027, while 90 business days (Monday to Friday) later is Tuesday, March 16, 2027. Add or subtract any mix of years, months, weeks and days to get the date and its weekday.

- Interactive calculator: https://calculatorswithsteps.com/date-calculator
- Category: Date & Time Calculators
- Last updated: 2026-11-10
- Publisher: Calculators With Steps (calculatorswithsteps.com)

## How to use the date calculator

1. Enter the **start date**. It defaults to today, so the tool works as a "date from today" calculator straight away.
2. Choose **Add** to go forward in time or **Subtract** to go back.
3. Type any combination of **years, months, weeks and days**. Leave the ones you don't need at zero.
4. Tick **business days only** if the Days part should skip Saturdays and Sundays, for a delivery estimate or a notice period counted in working days.

The result shows the new date and its weekday, how many calendar days and weeks it is from the start, the number of business days crossed, the day of the year and the ISO week number. The step-by-step box lists each stage so you can check it by hand.

## How the date calculation works

Adding days is simple counting. Each date is converted to a day number, the days are added, and the total is converted back to a calendar date. Because the arithmetic uses whole calendar days, daylight-saving changes cannot push the answer forward or back by a day.

Months and years are different because they are not a fixed number of days. A month can have 28, 29, 30 or 31 days. So the calculator moves the month and year first and keeps the same day of the month:

**New date = start date + years and months (same day of month) + weeks × 7 days + days**

If that day does not exist in the target month, the date moves back to the last day of the month. This is the same rule Excel's EDATE function uses. Weeks and days are then added as ordinary days.

## Worked examples

All of these start on Tuesday, November 10, 2026, unless noted.

| Calculation | Result | Weekday |
| --- | --- | --- |
| + 30 days | December 10, 2026 | Thursday |
| + 60 days | January 9, 2027 | Saturday |
| + 90 days | February 8, 2027 | Monday |
| + 120 days | March 10, 2027 | Wednesday |
| + 180 days | May 9, 2027 | Sunday |
| + 1 year, 2 months, 3 weeks, 4 days | February 4, 2028 | Friday |
| − 45 business days | September 8, 2026 | Tuesday |

Ninety days from November 10, 2026 lands in week 6 of 2027 and crosses 64 weekdays. If you are counting a 90-day return window or a probation period, check whether your policy counts calendar days or working days, because the two answers are weeks apart.

## Month-end dates and leap years

Month arithmetic is where most date mistakes happen:

- **January 31 + 1 month** gives February 28, 2027, or February 29, 2028 in a leap year.
- **August 31 − 6 months** gives February 28, 2026.
- **February 29, 2028 + 1 year** gives February 28, 2029, since 2029 has no leap day.

A leap year has 366 days. Under the Gregorian calendar a year is a leap year if it divides by 4, except century years, which must divide by 400. So 2000 and 2028 are leap years and 2100 is not.

One side effect is that month steps don't always reverse. January 31 plus one month is February 28, but February 28 minus one month is January 28. If you need a fixed number of days, enter days instead of months.

## Business days and deadlines

With the business days option ticked, the Days part counts only Monday to Friday. Starting on a Friday, one business day later is the following Monday. Ten business days after Friday, November 13, 2026 is Friday, November 27, 2026.

Public holidays differ by country, state and employer, so the calculator does not remove them. Add one day for each holiday that falls inside your range. For the number of days between two dates you already know, use the [days between dates calculator](https://calculatorswithsteps.com/days-between-dates-calculator) instead.

## Date formulas in Excel and Google Sheets

Spreadsheets store dates as serial numbers, so the same logic works there:

- `=A1+90` adds 90 days to the date in A1.
- `=A1-30` goes back 30 days.
- `=EDATE(A1,6)` adds six months and clamps month-end dates.
- `=WORKDAY(A1,10)` adds ten working days. A third argument can list holiday dates to skip.
- `=TEXT(A1,"dddd")` shows the weekday name.

## Tips

- To find a date of birth from an age, subtract the age in years from today, then check the exact day with the [age calculator](https://calculatorswithsteps.com/age-calculator).
- For pregnancy dates, the [due date calculator](https://calculatorswithsteps.com/due-date-calculator) adds 280 days to the first day of the last period.
- To add hours and minutes rather than days, use the [time calculator](https://calculatorswithsteps.com/time-calculator).

## Frequently asked questions

### How do I add days to a date?

Enter the start date, choose Add, and type the number of days. The calculator counts forward one calendar day at a time, so 90 days after November 10, 2026 is Monday, February 8, 2027.

### What is 30, 60 or 90 days from a date?

Counting from November 10, 2026, 30 days later is Thursday, December 10, 2026, 60 days later is Saturday, January 9, 2027, and 90 days later is Monday, February 8, 2027. Change the start date above to get the answer for your own date.

### What is one month after January 31?

February has no 31st, so the result moves back to the last day of February. January 31, 2027 plus one month is February 28, 2027, and January 31, 2028 plus one month is February 29, 2028 because 2028 is a leap year.

### How do I subtract months from a date?

Choose Subtract and enter the months. Six months before August 31, 2026 is February 28, 2026, again because February has no 31st.

### How do I add business days only?

Tick the business days box and the Days part skips Saturdays and Sundays. Ten business days after Friday, November 13, 2026 is Friday, November 27, 2026, which skips four weekend days. Public holidays are not skipped, so add them yourself.

### How do I calculate a date in Excel?

Put the start date in cell A1. =A1+90 adds 90 days, =EDATE(A1,3) adds three months and =WORKDAY(A1,10) adds ten working days. Format the answer cell as a date if it shows a serial number.

### In what order are years, months, weeks and days added?

Years and months are added first, then weeks, then days. One year, two months, three weeks and four days after November 10, 2026 is Friday, February 4, 2028, which is 451 days later.

## Sources

- [Microsoft Support – EDATE function (add months to a date)](https://support.microsoft.com/en-us/office/edate-function-3c920eb2-6e66-44e7-a1f5-753ae47ee4f5)
- [Microsoft Support – WORKDAY function (add working days)](https://support.microsoft.com/en-us/office/workday-function-f764a5b7-05fc-4494-9486-60d494efbf33)
- [Wikipedia – ISO week date](https://en.wikipedia.org/wiki/ISO_week_date)